Joining of structural members by welding

ABSTRACT

A method of manufacturing a structural assembly is provided. In one embodiment, the method includes the steps of providing first and second structural members having preselected shapes and dimensions. The first structural member defines a first raised portion and the second structural member defines a second raised portion. According to one embodiment, the providing step includes forming the first and second structural members into preselected shapes and dimensions. The first and second structural members can comprise plates, T-stiffeners or tubular members. The first raised portion of the first structural member is positioned adjacent to the second raised portion of the second structural member following the providing step to thereby define an interface therebetween and wherein the first and second raised portions define a substantially consumable weld land. Thereafter, the first and second structural members are irradiated with a high-energy source along the interface to thereby substantially consume the weld land and join the first and second structural members to form a structural assembly. The first high-energy source preferably comprises an electron beam or a laser.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.09/966,969, filed Sep. 28, 2001 now U.S. Pat. No. 6,483,069, whichclaims the benefit of U.S. Provisional Application No. 60/237,281, filedOct. 2, 2000.

FIELD OF THE INVENTION

The present invention relates to structural assemblies and, moreparticularly, relates to the joining of structural members by welding toform structural assemblies.

BACKGROUND OF THE INVENTION

Conventional structural assemblies, as used in the manufacture ofmilitary and commercial aircraft and missiles, are commonly formed oflightweight, high strength materials such as aluminum, aluminum alloys,titanium and titanium alloys. These assemblies are commonly constructedusing a bonded honeycomb-sandwich construction or a built-up structurefrom structural members that are fabricated using manufacturing methodssuch as a machined die-forging, investment casting or hogout machiningfrom stock material. Conventional structural assemblies formed fromthese types of constructions generally include large numbers of partsand fasteners that can result in extensive tooling and increased laborcosts during manufacture and assembly.

During use, aircraft structural assemblies are subjected to a variety ofenvironmental conditions, temperature variations, severe acoustic andvibration environments, all of which create mechanical and thermalstresses. Over time, the application of cyclical stresses to bondedstructural assemblies can lead to disbanding at the joints, and unlessrepaired, it can result in mechanical failure. Due to the large numberof parts and fasteners utilized in the construction of conventionalstructural assemblies, maintenance and repair can be time consuming andlabor intensive, which can be costly over the life of the assembly. Thenumber of total parts utilized in a bonded honeycomb or built-upstructure can also increase the overall weight of the aircraft.Consequently, conventional structural assemblies are generally costly tobuild and maintain and can adversely affect the weight of the aircraft.

In seeking better structural assembly designs, other types of joiningmethods have been proposed for assembling the component parts of thestructural assemblies. For example, one such alternative joining methodincludes full penetration electron beam welding which produces anautogenous weld. Structural members joined by electron beam welding arefused together using the heat generated by a concentrated beam ofhigh-velocity electrons impinging on the adjoining surfaces of thestructural members. The kinetic energy of the electrons is convertedinto heat as the electrons strike the structural members. Electron beamwelding is typically conducted under a high vacuum using an electronbeam gun column to create and accelerate the beam of electrons, as isknown in the art. The electron beam gun column generally includes anelectron gun, which is comprised of an emitter, a bias electrode, and ananode, and ancillary components, such as beam alignment, focus anddeflection coils. The high-energy density in the focused electron beamproduces deep, narrow welds at high speeds, with minimum distortion andother deleterious heat effects to the structural members. For example,depth-to-width ratios for electron beam welds typically range between10:1 and 30:1 with welding speeds as high as 200 mm/s (40 ft/min).Electron beam welds exhibit superior strength compared with welds formedusing other fusion welding processes.

One technique of full penetration electron beam welding is referred toas the keyhole technique in which the electron beam creates a holeentirely through the structural members to be joined. The hole createdby the electron beam is subsequently filled with molten metal as thebeam moves along the interface defined by the adjacent structuralmembers. Referring to FIG. 1A, there is illustrated one embodiment ofthe keyhole technique. As the electron beam 10 having a diameter D ismoved along the interface or joint 12 between the structural members 14a, 14 b, as indicated by the directional arrow 11, the molten metal isforced around the sides of the beam from the leading side 15 a to thetrailing side 15 b where the metal solidifies to form the weld bead 16.

As illustrated in FIGS. 1A and 1B, due to spatter, bead fall through,and/or vaporization of the metal during welding or weld shrinkage uponcooling, there may be insufficient material to completely fill thekeyhole as the electron beam 10 moves along the interface 12 between thestructural members 14 a, 14 b, which can result in regions of underfillor undercut 18 within the solidified weld bead 16. The volume ofunderfill or undercut 18 increases when, as illustrated in FIG. 2, theelectron beam 10 moves through a section of the structural members 14 a,14 b where the thickness of the structural members decreases from athickness of t₂ to a thickness of t₁, as represented by t_(δ). Since thevolume of material on the leading side 15 a of the electron beam 10 isless than the volume of material on the trailing side 15 b of the beam,there is insufficient material to fill the keyhole as the electron beammoves through the structural members.

In order to compensate for any underfilling or undercutting duringelectron beam welding, conventional structural members 24 a, 24 b aretypically fabricated with a raised portion 20 a, 20 b along the side ofeach structural member to be welded, as illustrated in FIG. 3. When thestructural members are positioned adjacent to one another prior towelding, the raised portions 20 a, 20 b collectively form a weld land20. As illustrated by the weld profile in FIG. 3, any underfilling orundercutting during electron beam welding of the structural members 24a, 24 b occurs within the weld land 20 of the structural assembly 22.Once the structural members are joined together by the electron beam,the weld land 20 is removed from the structural assembly 22 using knownmechanical machining processes, such as using cutting or grinding tools,to thereby provide a structural assembly having a smooth finishedsurface. While the weld land 20 prevents underfilling or undercuttingwithin the weld bead 16 joining the structural members, the formationand removal of the weld land significantly increase the material, laborand tooling costs associated with the manufacture of the structuralassembly.

As a result, there remains a need for an improved method of constructingstructural assemblies, which minimizes the costs associated withmanufacture and assembly of the structural assemblies, as well asreduces the overall weight of the aircraft. The structural assembliesmust also be capable of providing high mechanical strength andstructural rigidity.

SUMMARY OF THE INVENTION

The present invention provides a method of manufacturing a structuralassembly including the steps of providing first and second structuralmembers having preselected shapes and dimensions. The first structuralmember defines a first raised portion and the second structural memberdefines a second raised portion. According to one embodiment, theproviding step includes forming the first and second structural membersinto preselected shapes and dimensions. The forming step can includecasting, forging or machining the first and second structural members.According to another embodiment, the first and second structural memberscomprise plates, T-stiffeners or tubular members. According to stillanother embodiment, the first and second structural members are formedof aluminum, an aluminum alloy, titanium or a titanium alloy. The firstraised portion of the first structural member is positioned adjacent tothe second raised portion of the second structural member following theproviding step to thereby define an interface therebetween and whereinthe first and second raised portions define a substantially consumableweld land. Thereafter, the first and second structural members areirradiated with a high-energy source along the interface to removesurface irregularities that cause stress concentrations. The firsthigh-energy source can include an electron beam or a laser.Advantageously, the consumed weld land does not require a post-weldmechanical machining step in order to provide a finished surface.

According to another embodiment, the method of manufacturing thestructural assembly includes the steps of determining the shape anddimensions of a weld land based upon the shape and dimensions of firstand second structural members such that the weld land will besubstantially consumable, but provide sufficient material to negate anyunderfill in the base geometry. The first and second structural membersare then provided having the preselected shapes and dimensions.According to one embodiment, the providing step includes forming thefirst and second structural members into the preselected shapes anddimensions. The forming step can include casting, forging or machiningthe first and second structural members. According to anotherembodiment, the first and second structural members comprise plates,T-stiffeners or tubular members. According to still another embodiment,the first and second structural members are formed of aluminum, analuminum alloy, titanium or a titanium alloy. The first structuralmember is then positioned adjacent to the second structural memberfollowing the providing step to thereby define an interface therebetweenand wherein the first and second structural members define thesubstantially consumable weld land. Thereafter, the first and secondstructural members are irradiated with a high-energy source along theinterface to thereby substantially consume the weld land and join thefirst and second structural members to form a structural assembly.Preferably, the first high-energy source comprises an electron beam or alaser.

In still another embodiment, the structural assembly is irradiated alongthe interface with a second high-energy source after the firstirradiating step to remove any stress concentration details and therebyprovide a finished surface having improved fatigue characteristics.Preferably, the second high-energy source comprises a laser. Thestructural assembly can then be secured to other structural assembliesto form the frame of an aircraft.

The present invention also provides a structural assembly including afirst structural member defining a first surface and a second structuralmember positioned adjacent the first structural member. In oneembodiment, the first and second structural members comprise plates,T-stiffeners or tubular members. In another embodiment, the first andsecond structural members are formed of aluminum, an aluminum alloy,titanium or a titanium alloy. The second structural member defines afirst surface corresponding to and substantially planar with the firstsurface of the first structural member. The structural assembly includesa weld joint which joins the first and second structural members.Advantageously, the weld joint is formed by irradiating the first andsecond structural members with a high-energy source such that a surfaceof the weld joint is substantially planar with the first surfaces of thefirst and second structural members and such that no further processingof the weld joint is necessary to create the substantially planarsurface of the weld joint. In another embodiment, the first and secondstructural members each define corresponding second surfaces. Accordingto this embodiment, the weld joint defines a second surfacecorresponding to and substantially planar with the second surfaces ofthe first and second structural members.

Accordingly, there has been provided a structural assembly and anassociated method of manufacture allowing for the efficient constructionof aircraft structural assemblies, which requires less stock materialand takes less time to manufacture and assemble. The resultantassemblies include an autogenous weld having high mechanical strengthand structural rigidity

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages and features of the invention, andthe manner in which the same are accomplished, will become more readilyapparent upon consideration of the following detailed description of theinvention taken in conjunction with the accompanying drawings, whichillustrate preferred and exemplary embodiments, and which are notnecessarily drawn to scale, wherein:

FIG. 1A is a plan view illustrating the keyhole technique of electronbeam welding, as is known in the art;

FIG. 1B is a cross-sectional view along lines 1B—1B in FIG. 1Aillustrating underfilling and/or undercutting in the weld bead, as inknown in the art;

FIG. 2 is a cross-sectional view illustrating the keyhole technique ofelectron beam welding on adjacent structural members in which thethickness of the structural members is decreasing, as is known in theart;

FIG. 3 is a cross-sectional view illustrating underfilling andundercutting in a weld land, as is known in the art;

FIG. 4A is a cross-sectional view defining relevant variables andillustrating the positioning of the first and second structural membersprior to electron beam welding to thereby define a substantiallyconsumable weld land, according to one embodiment of the presentinvention;

FIG. 4B is a cross-sectional view illustrating the substantiallyconsumed weld land of a structural assembly formed by electron beamwelding the first and second structural members of FIG. 4A;

FIG. 4C is a cross-sectional view illustrating the structural assemblyof FIG. 4B after undergoing laser glazing to remove any remaining stressconcentration details;

FIG. 5A is a perspective view illustrating the positioning of the firstand second structural members of a T-stiffened cross section prior toelectron beam welding to thereby define a substantially consumable weldland, according to another embodiment of the present invention;

FIG. 5B is a cross-sectional view illustrating the profile of the raisedportion of the first structural member of FIG. 5A;

FIG. 5C is a perspective view illustrating the substantially consumedweld land of a T-stiffened structural assembly formed by electron beamwelding the first and second structural members of FIG. 5A;

FIG. 6A is a cross-sectional view defining relevant variables andillustrating a first structural member, according to one embodiment ofthe present invention;

FIG. 6B is a cross-sectional view defining relevant variables andillustrating a structural assembly having a consumed weld land,according to one embodiment of the present invention;

FIG. 6C is a table listing the dimensions of square butt weld specimensfor optimizing the dimensions of the consumable weld land of FIG. 6B;

FIGS. 6D and 6J-6M are graphs illustrating the relationship between theheight h of the consumable weld land and the resultant height h₁, h₂ ofany remaining stress concentration details in the weld bead of FIG. 6B;

FIGS. 6E and 6N are graphs illustrating the relationship between thewidth w of the consumable weld land and the resultant height h₁, h₂ ofany remaining stress concentration details in the weld bead of FIG. 6B;

FIG. 6F is a graph illustrating the relationship between the width w ofthe consumable weld land and the areas A₂ and A₄ of any remaining stressconcentration details in the weld bead in FIG. 6B;

FIGS. 6G and 6O-6Q are graphs illustrating the relationship between theheight h of the consumable weld land and the areas A₂ and A₄ of anyremaining stress concentration details in the weld bead illustrated inFIG. 6B;

FIG. 6H is a graph illustrating the optimum height h and width w for theconsumable weld land having the shape illustrated in FIG. 4B;

FIG. 6I is a graph illustrating the optimum total thickness (h+t) of theweld land and base material illustrated as a function of the thickness tof the first and second structural members illustrated in FIG. 4A;

FIG. 7A is a cross-sectional view illustrating the movement of anelectron beam through a structural member in the shape of a T-stiffenerhaving preselected dimensions with no weld land;

FIG. 7B is a table listing the penetration thickness T of the electronbeam at various points as the beam moves along the length of theT-stiffener of FIG. 7A;

FIG. 7C is a graph illustrating the penetration thickness T measured inthe beam axis plotted as a function of the distance the beam travels asit moves along the length of the T-stiffener of FIG. 7A;

FIG. 7D is a graph illustrating the relationship between a base geometryand a new geometry that includes a substantially consumable weld landthat does not produce an underfill in the base material of an autogenouselectron beam weld;

FIG. 8 is a flow chart illustrating the operations for manufacturing thestructural assemblies of FIGS. 4C and 5C, according to one embodiment ofthe present invention; and

FIG. 9 is a flow chart illustrating the operations for manufacturing thestructural assemblies of FIGS. 4C and 5C, according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

Referring now to the drawings and, in particular, to FIGS. 4A, 4B, and4C, there is illustrated the construction of a structural assembly 32,according to one embodiment of the present invention. As illustrated inFIG. 4A, the structural assembly includes first and second structuralmembers 34 a, b positioned adjacent one another. The first and secondstructural members are each formed into a preselected shape orconfiguration through known manufacturing means, such as casting,machining and/or forging. The first and second structural members 34 a,b are preferably formed from a material having a high strength-to-weightratio, such as aluminum, an aluminum alloy, titanium or a titaniumalloy. In one embodiment, the first and second structural members areboth formed of Ti-6Al-4 v. The shape of the first and second structuralmembers 34 a, b may vary depending upon the particular serviceapplication and required mechanical properties of the structuralassembly 32. For example, the first and second structural members 34 a,b can be formed into plates 54, as illustrated in FIG. 4A, T-stiffeners,as illustrated in FIGS. 5A and 5B, or into tubular configurations (notshown).

The first and second structural members 34 a, b have preselecteddimensions, including thickness t, length L, width (not shown). Thedimensions of the structural members are likewise dependent upon theparticular service application and required mechanical properties of thestructural assembly 32. As illustrated in FIG. 4A, the first structuralmember 34 a defines at least one raised portion 30 a along the side 33 aof the first structural member that is to be joined to the secondstructural member 34 b. Similarly, the second structural member 34 bdefines at least one raised portion 30 b along the side 33 b of thesecond structural member that is to be joined to the first structuralmember. The location of the raised portions 30 a, b along the adjoiningsides 33 a, b of the first and second structural members can varydepending upon the shape and dimensions of the first and secondstructural members 34 a, b and depending upon the intensity of theelectron beam or laser, as well as the welding speed. For example, theraised portions 30 a, b may be located along only a select portion ofthe adjoining sides 33 a, b of the first and second structural members,as illustrated in FIG. 4A where the first and second structural membersdefine raised portions on only one side of each member, or the raisedportions may be located along a majority or even the entire perimeter ofthe adjoining sides of the structural members, as illustrated in FIG. 5Bwhere the first and second structural members define raised portionsalong the entire perimeter of the adjoining sides. In another embodiment(not shown), the first and second structural members each define aplurality of raised portions along the adjoining sides of the members,which raised portions are spaced from one another.

As illustrated in FIGS. 4A and 5A, prior to welding the first and secondstructural members 34 a, b to form the structural assembly 32, the firstraised portion 30 a of the first structural member is positionedadjacent to the second raised portion 30 b of the second structuralmember to define an interface 39 between the structural members. Whenpositioned adjacent one another, the first and second raised portions 30a, b collectively define a consumable weld land 40. As illustrated inFIGS. 4B and 5C, a consumable weld land 40 refers to a weld land that issubstantially consumed by the electron beam during welding such that thevolume of material represented by the weld land is utilized to fill anyunderfill or undercut in the autogenous weld bead 36. The election beamcan be generated from one of many commercially available electron beamwelders, such as a Sciaky 60 kV/42 kW electron beam welder.

As described above, preferably the weld land 40 is consumed and thefirst and second structural members 34 a, b are joined together using anelectron beam. However, the use of an electron beam to consume the weldland 40 and join the first and second structural members 34 a, b isdescribed for purposes of illustration only and not limitation. It isconsidered to be within the spirit and scope of the present invention toutilize other high-energy sources to irradiate the structural members 34a, b so as to consume the weld land 40 and join the structural members,including a laser or a plasma arc.

Referring to FIG. 4B, there is illustrated a consumed weld land 40according to one embodiment of the present invention. As illustrated inFIG. 4B, the first structural member 34 a of the structural assembly 32defines first and second surfaces 25, 27. Similarly, the secondstructural member 34 b of the structural assembly 32 defines first andsecond surfaces 26, 28 corresponding to, and substantially planar with,the respective first and second surfaces 25, 27 of the first structuralmember 34 a. The structural assembly includes a weld joint or weld bead36, which joins the first and second structural members 34 a, b. Asdescribed above, the weld bead 36 is formed by irradiating the first andsecond structural members 34 a, b with a high-energy source, such as anelectron beam, a laser or a plasma arc, such that at least one surface37 of the weld joint is substantially planar with the first surfaces 25,26 of the first and second structural members 34 a, b and such that nofurther processing of the weld joint is necessary to create thesubstantially planar surface of the weld joint 36. Preferably, the weldbead 36 also defines a second surface 42 corresponding to andsubstantially planar with the second surfaces 27, 28 of the first andsecond structural members 34 a, b.

Advantageously, as illustrated in FIG. 4C, a substantially consumed weldland 40 or weld bead 36 can be finished, if necessary, by glazing bothsides of the weld bead 36 with a laser, as opposed to machining the weldbead, to remove any remaining stress concentration details and therebyprovide a smooth finished surface having improved fatiguecharacteristics. The laser beam can be generated from one of manycommercially available lasers, such as a Hoss 3 kW Nd:YAG Laserinstalled on a Fanuc M 710 I; 6 Axis NC controlled robot. Thus, thesubstantially consumed weld land 40 eliminates the post-weld machiningstep thereby reducing the overall manufacturing costs of the structuralassembly 32.

The shape and dimensions of the consumable weld land 40 and, thus, theraised portions 30 a, b defined by the first and second structuralmembers 34 a, b, are based primarily upon the shape and dimensions ofthe first and second structural members. FIGS. 6A, 6B, 6C, and 6Dillustrate the steps for determining the optimum dimensions of asubstantially consumable weld land 40, according to one embodiment ofthe present invention, such that the volume of material represented bythe weld land is utilized to fill any underfill or undercut in theautogenous weld bead 36. Referring to FIGS. 4A and 6A, there isillustrated one embodiment of a first structural member 34 a comprisinga plate 54 having a width (not shown), length L and a thickness t. Theplate 54 defines a raised portion 30 a having a width w, height h, andradius R. As discussed above, prior to welding the first and secondstructural members 34 a, b to form the structural assembly 32, the firstraised portion 30 a of the first structural member is positionedadjacent to the second raised portion 30 b of the second structuralmember to define an interface 39 between the structural members and todefine the consumable weld land 40. As illustrated in FIGS. 4B and 6B,the first and second structural members 34 a, b are then joined togetherto form a structural assembly 32 by irradiating the first and secondstructural members with a high-energy source along the interface 39 tothereby substantially consume the weld land 40. After welding theconsumable weld land 40, there may exist minor stress concentrationdetails 53 having an area designated A₁ and A₃, respectively, in theweld bead 36 of the structural assembly 32. As discussed above andillustrated in FIG. 4C, the weld bead 36 formed by the substantiallyconsumed weld land 40 can be finished by glazing both sides of the weldbead 36 with a laser, as opposed to machining the weld bead, to removeany remaining minor stress concentration details and thereby provide asmooth finished surface having improved fatigue characteristics.

FIG. 6C illustrates a square butt weld matrix for thirty-four specimensof the first and second structural members 34 a, b illustrated in FIGS.4A and 6A in which the thickness t of the structural members and theheight h, width w and radius R of the raised portions 30 a, b werevaried as indicated. The first and second structural members were joinedby full-penetration autogenous electron beam welding to form thestructural assembly 32 illustrated in FIG. 6B. Referring to FIG. 6D,there is illustrated graphically the relationship between the height hof the consumable weld land 40 shown in FIG. 4A and the resultant heighth₁, h₂ of any remaining stress concentration details 53 in the weld bead36 shown in FIG. 6B, where the thickness t of the structural members 34a, b was maintained constant at approximately t=0.4 inches (10.16 mm);and the width w and radius R of the raised portions 30 a, b weremaintained constant at approximately w=0.05 inches (1.27 mm) and R=0.25inches (6.35 mm). FIGS. 6J, 6K, 6L, and 6M illustrate similar graphicalrelationships between the height h of the consumable weld land 40 shownin FIG. 4A and the resultant height h₁, h₂ of any remaining stressconcentration details 53 in the weld bead 36 shown in FIG. 6B for otherconstant values of thickness t, width w and radius R.

Similarly, FIG. 6E illustrates graphically the relationship between thewidth w of the consumable weld land 40 shown in FIG. 4A and theresultant height h₁, h₂ of any remaining stress concentration details 53in the weld bead 36 shown in FIG. 6B, where the thickness t of thestructural members 34 a, b was maintained constant at approximatelyt=0.4 inches (10.16 mm); and the height h and radius R of the raisedportions 30 a, b were maintained constant at approximately h=0.1 inches(2.54 mm) and R=0.25 inches (6.35 mm). FIG. 6N illustrates a similargraphical relationship between the width w of the consumable weld land40 shown in FIG. 4A and the resultant height h₁, h₂ of any remainingstress concentration details 53 in the weld bead 36 shown in FIG. 6B,where the thickness t of the structural members 34 a, b was maintainedconstant at approximately t=0.1 inches (10.16 mm); and the height h andradius R of the raised portions 30 a, b were maintained constant atapproximately h=0.04 inches (2.54 mm) and R=0.25 inches (6.35 mm).

FIG. 6F illustrates graphically the relationship between the width w ofthe consumable weld land 40 shown in FIG. 4A and the areas A₂ and A₄ ofany remaining stress concentration details 53 in the weld bead 36 shownin FIG. 6B, where the thickness t of the structural members 34 a, b wasmaintained constant at approximately t=0.4 inches (10.16 mm); and theheight h and radius R of the raised portions 30 a, b were maintainedconstant at approximately h=0.1 inches (2.54 mm) and R=0.25 inches (6.35mm).

FIG. 6G illustrates graphically the relationship between the height h ofthe consumable weld land 40 shown in FIG. 4A and the areas A₂ and A₄ ofany remaining stress concentration details 53 in the weld bead 36, wherethe thickness t of the structural members 34 a, b was maintainedconstant at approximately t=0.4 inches (10.16 mm); and the width w andradius of curvature R of the raised portions 30 a, b were maintainedconstant at approximately w=0.05 inches (1.27 mm) and R=0.25 inches(6.35 mm). FIGS. 6O, 6P, and 6Q illustrate similar graphicalrelationships between the height h of the consumable weld land 40 shownin FIG. 4A and the areas A₂ and A₄ of any remaining stress concentrationdetails 53 in the weld bead 36, for other constant values of thicknesst, width w and radius R. From the data presented above in FIGS. 6C-6Gand 6J-6Q, the optimum height h and width w for the consumable weld landcan be determined. The results of these determinations are presented inFIGS. 6H and 6I.

FIGS. 7A, 7B, 7C, and 7D illustrate the steps for determining theapproximate volume of a substantially consumable weld land 40 for aT-stiffener 44, according to another embodiment of the presentinvention. Referring to FIG. 7A, there is illustrated one embodiment ofa T-stiffener 44 where t_(web)=t_(stiffener)=R=1.0 inch (2.54 cm) andh=3 inches (7.62 cm). The penetration thickness of an electron beam 10impinging upon the surface of the T-stiffener at an angle ofapproximately θ=45° is summarized in FIG. 7B for the points or cutsthrough the structural member designated by the letters a-f along thelength of the T-stiffener. The penetration thickness is measured at thecenter of the electron beam and is measured in the beam axis andincludes the penetration of both the web 41 and stiffener 47, whereapplicable. At point a the penetration thickness is equal tot_(web)/cos(θ). At points b and c the penetration thickness is equal to(t_(web)+t_(stiffener))/cos(θ). At point d, the electron beam is tangentto the entry radius, which represents the maximum penetration thicknessand corresponds to the transition from increasing thickness todecreasing thickness. At point f the penetration thickness is againequal to t_(web)/cos(θ). This analysis of the T-stiffener does notinclude allowance for gaps, mismatches, material vaporization, bead fallthrough, beam tracking errors or spatter. However, it has been foundthat material vaporization is for the most part insignificant and thatbead fall through is relatively consistent along the weld bead.

FIG. 7C illustrates graphically the penetration thickness T of theelectron beam measured in the beam axis 10 plotted as a function of thedistance the beam travels as the beam moves along the length of theT-stiffener 44, as indicated by the directional arrow 11, where thedistance the beam travels is denoted the “beam run {X}.” The graphicalrepresentation in FIG. 7C illustrates the transition from the region ofincreasing thickness for the T-stiffener 44 between points a and d tothe region of decreasing thickness between points d and f. Thepenetration thickness of the electron beam is represented in equation(1) where, as discussed above, T is the penetration thickness along thecentral axis of the beam and X is in the beam run direction. Anapproximation of the base geometry thickness f(X) can be determinedusing known mathematical techniques, for example, computer aided linearregression or Fourier analysis.

T=f(X)   (1)

The rate of change of the electron beam penetration thickness in thebase geometry T at any point can be represented by the derivative ofequation (1):

ΔT=f′(X)  (2)

Referring to FIG. 7D, there is illustrated a section of the curve ofFIG. 7C. Using the diameter of the beam d_(beam), a triangle can beconstructed between the points represented by (X_(t), T_(t)), whereX_(t) is the location of the trailing edge of the electron beam andT_(t) is the penetration thickness of the trailing edge of the electronbeam, (X_(l), T_(l)), where X_(l) is the location of the leading edge ofthe electron beam and T_(l) is the penetration thickness of the leadingedge of the electron beam, and (X_(l), T_(t)). This triangle representsapproximately the minimum area of additional material A required toprevent underfill or undercut of the weld bead. The area of additionalmaterial A can then be multiplied by the diameter d_(beam) of theelectron beam to obtain the requisite volume of the consumable weldland. By performing this operation over the entire curve represented byequation (1), it is possible to generate the following equationrepresenting the new geometry (weld land+base thickness) g(X), where Crepresents the material required to account for vaporization, spatter,bead fall through, etc.

g(X)=f(X)+f′(X)d _(beam) +C  (3)

Based upon equation (3), the dimensions of a consumable weld land can bedetermined for the first and second structural members.

Referring now to FIG. 8, there is illustrated the operations performedto manufacture a structural assembly according to one embodiment of thepresent invention. The first step includes providing first and secondstructural members having preselected shapes and dimensions. The firststructural member defines a first raised portion and the secondstructural member defines a second raised portion. See block 60.According to one embodiment, the providing step includes forming thefirst and second structural members into preselected shapes anddimensions. See block 61. The forming step can include casting, forgingor machining the first and second structural members. See block 62. Thefirst raised portion of the first structural member is positionedadjacent to the second raised portion of the second structural memberfollowing the providing step to thereby define an interface therebetweenand wherein the first and second raised portions define a substantiallyconsumable weld land. See block 63. Thereafter, the first and secondstructural members are irradiated with a high-energy source along theinterface to thereby substantially consume the weld land and join thefirst and second structural members to form a structural assembly. Seeblock 64. Advantageously, the consumed weld land does not require apost-weld mechanical machining step in order to provide a finishedsurface. According to one embodiment, the structural assembly isirradiated along the interface with a second high-energy source afterthe first irradiating step to remove any stress concentration detailsand thereby provide a finished surface having improved fatiguecharacteristics. See block 65. The structural assembly can then besecured to other structural assemblies to form the frame of an aircraft.See block 66.

According to another embodiment, the method of manufacturing thestructural assembly includes the steps of determining the shape anddimensions of a weld land based upon the shape and dimensions of firstand second structural members such that the weld land will besubstantially consumable. See block 70. The first and second structuralmembers are then provided having the preselected shapes and dimensions.See block 71. According to one embodiment, the providing step includesforming the first and second structural members into the preselectedshapes and dimensions. See block 72. The forming step can includecasting, forging or machining the first and second structural members.See block 73. The first structural member is then positioned adjacent tothe second structural member following the providing step to therebydefine an interface therebetween and wherein the first and secondstructural members define the substantially consumable weld land. Seeblock 74. Thereafter, the first and second structural members areirradiated with a high-energy source along the interface to therebysubstantially consume the weld land and join the first and secondstructural members to form a structural assembly. Preferably, the firsthigh-energy source comprises an electron beam. See block 75. Accordingto one embodiment, the structural assembly is irradiated along theinterface with a second high-energy source after the first irradiatingstep to remove any stress concentration details and thereby provide afinished surface having improved fatigue characteristics. See block 76.The structural assembly can then be secured to other structuralassemblies to form the frame of an aircraft. See block 77.

Accordingly, there has been provided a method of manufacturing astructural assembly allowing for the efficient construction of aircraftstructural assemblies, which requires less stock material and takes lesstime to manufacture and assemble. It has been estimated that theconsumable weld land of the present invention will reduce the overallmanufacturing costs of structural assemblies by approximately fortypercent in terms of reduced material usage and labor and toolingexpenses. Additionally, the resultant structural assemblies include anautogenous weld having high mechanical strength and structural rigidity

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A structural assembly, comprising: a firststructural member defining a first surface; a second structural memberpositioned adjacent said first structural member, said second structuralmember defining a first surface corresponding to and substantiallyplanar with said first surface of said first structural member; and aweld joint which joins said first and second structural members, saidweld joint comprises only a substantially consumed weld land defined bysaid first and second structural members without underfilling orundercutting, said weld joint being formed by irradiating said first andsecond structural members with a high-energy source such that a surfaceof said weld joint is substantially planar with said first surfaces ofsaid first and second structural members and such that no furtherprocessing of said weld joint is necessary to create said substantiallyplanar surface of said weld joint.
 2. The structural assembly of claim 1wherein said first and second structural members each definecorresponding second surfaces, and wherein said weld joint defines asecond surface corresponding to and substantially planar with saidsecond surfaces of said first and second structural members.
 3. Thestructural assembly of claim 1 wherein said first and second structuralmembers each comprises a member selected from the group consisting of aplate, a stiffener and a tubular member.
 4. The structural assembly ofclaim 1 wherein said first and second structural members are formed ofmaterials selected from the group consisting of aluminum, an aluminumalloy, titanium and a titanium alloy.
 5. A structural assembly formed byconsuming a weld land, comprising: a first structural member defining afirst surface; a second structural member positioned adjacent said firststructural member, said second structural member defining a firstsurface corresponding to and substantially planar with said firstsurface of said first structural member; and a weld joint which joinssaid first and second structural members, said weld joint comprisingonly a substantially consumed weld land defined by said first and secondstructural members without underfilling or undercutting, said weld jointbeing formed by irradiating said first and second structural memberswith a high energy source so as to substantially consume the weld landdefined thereon and wherein a surface of said weld joint issubstantially planar with said first surfaces of said first and secondstructural members.
 6. The structural assembly of claim 5 wherein saidfirst and second structural members each define corresponding secondsurfaces, and wherein said weld joint defines a second surfacecorresponding to and substantially planar with said second surfaces ofsaid first and second structural members.
 7. The structural assembly ofclaim 5 wherein said first and second structural members each comprisesa member selected from the group consisting of a plate, a T-stiffenerand a tubular member.
 8. The structural assembly of claim 5 wherein saidfirst and second structural members are formed of materials selectedfrom the group consisting of aluminum, an aluminum alloy, titanium and atitanium alloy.
 9. A structural assembly comprising first and secondstructural members and a weld joint which joins said first and secondstructural members, said weld joint comprising only a substantiallyconsumed weld land defined by said first and second structural memberswithout underfilling or undercutting, the structural assembly beingmanufactured by a process comprising the steps of: providing first andsecond structural members, wherein the first structural member defines afirst raised portion and the second structural member defines a secondraised portion; positioning the first raised portion of the firststructural member adjacent to the second raised portion of the secondstructural member following said providing step to thereby define aninterface therebetween and wherein the first and second raised portionsdefine a substantially consumable weld land; and thereafter, irradiatingthe first and second structural members with a high-energy source alongthe interface to thereby substantially consume the weld land and jointhe first and second structural members to form a structural assembly.10. A structural assembly manufactured according to the process of claim9 wherein the high-energy source comprises a source selected from thegroup consisting of an electron beam and a laser.
 11. A structuralassembly manufactured according to the process of claim 9, furthercomprising irradiating the structural assembly along the interface witha second high-energy source after said first irradiating step to removeany stress concentration details and thereby provide a finished surfacehaving improved fatigue characteristics.
 12. A structural assemblymanufactured according to the process of claim 11 wherein the secondhigh-energy source comprises a laser.
 13. A structural assemblymanufactured according to the process of claim 9 wherein the first andsecond structural members each comprises a member selected from thegroup consisting of a plate, a T-stiffener and a tubular member.
 14. Astructural assembly manufactured according to the process of claim 9wherein said providing step comprises forming the first and secondstructural members.
 15. A structural assembly manufactured according tothe process of claim 14 wherein said forming step comprises a methodselected from the group consisting of casting, forging and machining.16. A structural assembly manufactured according to the process of claim9 wherein the first and second structural members are formed ofmaterials selected from the group consisting of aluminum, an aluminumalloy, titanium and a titanium alloy.
 17. A structural assemblymanufactured according to the process of claim 9 further comprisingsecuring the structural assembly to other structural assemblies to formthe frame of an aircraft.
 18. A structural assembly manufacturedaccording to the process of claim 9 further comprising determining theshape and dimensions of the weld land based upon the shape anddimensions of the first and second structural members such that the weldland will be substantially consumable.